Which version of the Fox .40 is it? The BB ABC Deluxe or one of the Meehanite (Iron) Piston ones?
Or do you have one of the early "B" frame units? (same crankcase as the .45 and .46)

Fox's are all designed for LOW nitro- around 5 - 10% and if you have one of the cast iron piston ones, 17-20% CASTOR Oil in the fuel, no Synthetic.
You can get away with Castor/Synthetoc mix in the ABC version.

According to the manual for the Eagle .60, only 5% Nitro is required, unless you live at high altitudes or in very cold conditions, where a little more will assist starting.
25% would blow the thing apart.


If you go to
http://web.archive.org/web/200503060...m/manuals.html
you can still download the various manuals in .pdf format.

You mention the high speed and low speed needles. This indicates you have a very early engine as Fox have been only using air bleed carby's (single needle) for a long time now.